This application claims the priority of Korean Patent Application No. 2002-65175 filed on Oct. 24, 2002 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a method and an apparatus for detecting the fault of an optical switch, and more particularly, to a method and an apparatus for determining whether an optical switch malfunctions by detecting output power transitions of optical monitoring=signals from output ports of the optical switch.
2. Description of the Related Art
Conventional arts methods for monitoring the fault of an optical switch include the steps of: applying different frequency tones in a frequency band of several kHz to several tens of kHz to each of the optical signals to be transmitted to input ports of the optical switch, splitting a portion of optical signals output from output ports of the optical switch, detecting tone information from the split portion of optical signals, comparing the detected tone information with switch configuration information, and determining whether the optical switch malfunctions. Here, the applying of frequency tone indicates sinusoidal amplitude modulation of input optical signal with a specific frequency using a low modulation coefficient within a range of 5% to minimize the bad influence on reception sensitivity.
A tone usually represents the pitch of voices of human beings or sound of musical instruments and refers to a constant frequency for a predetermined period of time. For example, the keys of a piano have their own tones.
In the field of present optical communications optical carriers with center frequency of more than 100 THz are on/off modulated within tens of GHz. These optical signals have frequency components of center frequency and the harmonics of on/off modulation frequency.
As described above, the tone applied optical signal contains an additional frequency (tone) component. Optical signals containing different tones may be applied to an optical switch, pass through switching channels, and portions of them are detected from output ports. In the prior art of tone applying, low frequency amplitude modulation is performed so that the amplitude of an optical signal is slightly fluctuated at that frequency. Here, actual information to be transmitted is transmitted with an amplitude-modulated portion of several tens of MHz to several GHz of the optical signal
The above-described prior art method can directly detect whether an optical switch malfunctions regardless of the type of switches. However, when applied tone components remain in an optical signal, which has passed through an optical system containing the optical switch such as an optical cross-connector (OXC), the fault detecting method using a tone cannot be applied to a next OXC. Also, the remaining tone components increase a transmission error rate in a final reception port. Thus, a complicated optical module has to be added to remove the used tone components after detecting the tones from all optical signals before the next optical switch. Even in this case, the quality deterioration of the optical signal cannot be completely prevented.